Simply said the ExceptionDate property in IExceptionOccurence specify the original time when the occurrence should occur if it wasn't an exception. In the given context:
a.) Create a recurring appointment (every day at 9:00)
b.) Changed one occurrence to 10:00
c.) Changed that occurrence to 11:00
there will be only one ExceptionOccurence with ExceptionDate : (date when occur) at 9:00. Changing the time when exception starts or ends doesn't affect the ExceptionDate.
Hope this information helps.
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